Research On Hybrid Precoding Techniques In Millimeter-Wave Massive MIMO Systems

In the 5th generation mobile communication system,the data transmission rate is required to reach the order of Gbps in order to meet the demand of large traffic mobile broadband services such as 3D ultra-high-definition video.In addition,the Internet of things service has led to an explosive increase in the number of network terminal.For the above reasons,the problem of the shortage of spectrum resources has become increasingly prominent.The millimeter-wave band has abundant spectrum resources and there are a large number of unlicensed bands which can be used free of charge without having to pay hige licensing fees.Therefore,millimeter-wave fundamentally solves the problem of spectrum resource shortage.However,millimeter wave signals are severely attenuated when they propagate in the atmosphere.Fortunately,due to the short wavelength of millimeter-wave signal and the small size of the corresponding antennas,the ultra high array gain can be obtained to compensate for the pass loss by deploying a massive multiple input multiple output(MIMO)systems.Thus,the combination of millimeter-wave and massive MIMO becomes inevitable.In order to improve the receiving performance of millimeter-wave massive MIMO systems,the base station can adopt precoding processing on the transmitted signal.Unlike the traditional MIMO system,which is completely precoded on the baseband,the millimeter-wave massive MIMO systems adopt a hybrid precoding architecture which combines digital precoding and radio frequency(RF)precoding.For this reason,this paper focuses on the hybrid precoding design for millimeter-wave massive MIMO systems.The main contents are as follows:1.In order to design the hybrid precoding in point-to-point scenarios,a hybrid precoding scheme that can effectively improve the spectral efficiency of the system is proposed using the idea of dictionary learning.The scheme firstly sparsely represents each column of the full digital precoding matrix.Then each dictionary atom is separated from the sparse representation by column and updated via performing singular value decomposition on the error matrix.Until the entire dictionary atoms are completely updated,the new dictionary matrix is achieved.Finally,the analog precoding matrix and digital precoding matrix can be obtained by sparsely reconstructing the full digital precoding matrix.Simulation results show that the proposed scheme greatly outperforms the hybrid precoding method based on orthogonal matching pursuit algorithm in terms of increasing spectrum efficiency and decreasing bit error rate.2.For the hybrid precoding design in multiuser scenarios,a low complexity hybrid precoding scheme based on hierarchical codebook is proposed.The scheme takes full advantage of the fact that the more antenna elements are formed,the narrower the formed beam is.Firstly,fewer antenna elements are configured to determine the coarse beam in theory,and a more refined beam is obtained by gradually doubling the antenna elements.Based on this,a hierarchical codebook based on beamsteering codebook is presented.Compared with the exhaustive search algorithm,it achieves a significant reduction in terms of the search complexity at the cost of less performance loss.Further,a hierarchical codebook of low resolution analog phase shifters(APSs)is also proposed in this paper.The simulation results show that the codebook inevitably leads to performance loss,but the problem of limited APSs resolution in actual communication scene is fully considered,and the APSs with different resolution can be configured flexibly according to the specific communication requirements.Therefore,this scheme is more practical.